The use of radars in industrial and automotive applications is evolving rapidly. Radars are used in many applications to detect target objects such as airplanes, military targets, vehicles, and pedestrians. Radar finds use in number of applications associated with a vehicle such as adaptive cruise control, collision warning, blind spot warning, lane change assist, parking assist and rear collision warning. Pulse radar and FMCW (Frequency Modulation Continuous Wave) radar are predominately used in such applications.
In a radar system, a local oscillator generates a transmit signal. The transmit signal is amplified and transmitted by one or more transmit units. In an FMCW radar, a frequency of the transmit signal is varied linearly with time. For example, the frequency of the transmit signal increases at a constant rate from 77 GHz to 81 GHz in 100 micro-seconds. This transmit signal is referred as a ramp signal or a chirp signal. One or more obstacles scatters the transmit signal. The scattered signal is received by one or more receive units in the radar system.
A signal obtained by mixing the transmitted signal and the received scattered signal is termed as a beat signal. The beat signal is sampled by an analog to digital converter (ADC) and processed by a processor to estimate a distance and a velocity of the one or more obstacles. The frequency of the beat signal is proportional to the range (distance) of the one or more obstacles.
For a moving obstacle, a phase of the beat signal varies across multiple ramp signals transmitted by the radar system. The frequency and phase of the beat signal from one or more receive units are analyzed by the processor to estimate the position and the velocity of the one or more obstacles.
The transmit signal from the local oscillator is provided to the one or more transmit units, and the one or more receiver units, which may be on one or multiple chips and/or semiconductor devices. The multiple transmit units and the multiple receive unit are required for beamforming. Beamforming requires signals transmitted by the multiple transmit units to be phase coherent.
A phase coherence between multiple transmit units is affected by routing delay mismatch. The one or more transmit or receive units may be located at different distances from the local oscillator which induces different routing delays in the transmit signal from the local oscillator to each transmit or receive unit. This routing delay mismatch causes errors in position and velocity estimation of the one or more obstacles.